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Peavey 115 BW and a JBL

jackietreehorn

jackietreehorn

Mar 31, 2020
64
91
Minneapolis, MN
#1
Hello. I got a really good deal on an unloaded Peavey 115 BW cab. I'd like to drop a JBL K140 into it.

I don't know the first thing about power handling and tuning bass cabs and what not and I've tried reading the threads, and here is what I know, vs what I've figured out:

The cabs dimensions are 27" x 24" x 12.5" and it has a 6" round port. My terrible math skills calculate the volume of the cab at 4.69 cubic feet.

I've read JBL recommends 4 cubic feet tuned to 40 hz.

Will this cab work alright? More importantly, if install the JBL into this cab and take it out for a test drive to see how it sounds, I'm not going to damage it am I? (Please forgive my complete ignorance on this subject). Thanks.
 
#2
How deep is the port. It’s unlikely that a 6” diameter port will work well unless the depth is quite long... maybe longer than the cabinet is deep.
 
#4
Net, the internal cabinet volume is around 4 cubic feet.

I looked up the JBL data (K-140-8 ohm) that I have and misremembered the opposite of what I had thought.

With the box you have, with a 6" diameter port the ideal port depth is ~1.5" which gives:

Mechanical power handling: ~250 watts RMS down to about 45Hz
F3=50Hz, F6=45Hz, F10=41Hz
Average sensitivity: ~98dB/1W/1M

This is actually pretty decent. With a 5" deep port:
Mechanical power handling: ~200 watts RMS down to about 45hz
F3=59Hz, F6=41hz and F10=36Hz

What this shows is that the driver benefits from a higher tuning in such a large box especially. The driver really does a little better overall in a 3CF box, but with the box you have it will be pretty decent with the 1.5" deep port.

This is not a monster driver, it's a medium power handling driver with decent sensitivity and a distinctive open mid voicing. This also assumes that it's either original soft parts or has been reconed with a kit that meets the factory specifications (possibly an incorrect assumption).

[correct model number typo]
 
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#8
agedhorse said:
Net, the internal cabinet volume is around 4 cubic feet.

I looked up the JBL data (K-120-8 ohm) that I have and misremembered the opposite of what I had thought.

With the box you have, with a 6" diameter port the ideal port depth is ~1.5" which gives:

Mechanical power handling: ~250 watts RMS down to about 45Hz
F3=50Hz, F6=45Hz, F10=41Hz
Average sensitivity: ~98dB/1W/1M

This is actually pretty decent. With a 5" deep port:
Mechanical power handling: ~200 watts RMS down to about 45hz
F3=59Hz, F6=41hz and F10=36Hz

What this shows is that the driver benefits from a higher tuning in such a large box especially. The driver really does a little better overall in a 3CF box, but with the box you have it will be pretty decent with the 1.5" deep port.

This is not a monster driver, it's a medium power handling driver with decent sensitivity and a distinctive open mid voicing. This also assumes that it's either original soft parts or has been reconed with a kit that meets the factory specifications (possibly an incorrect assumption).
Click to expand...
Isn’t the K-120 a 12” driver?
[Invalid or Expired Link Removed]
 
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#10
Depending on the year of the cab, they sound pretty decent with the 15" BW speaker. (at moderate volume) I bought one for old times sake recently just to leave at my church. (unless you're a young buck, you really don't want to schlep an old Peavey Cab):D I power mine with everything from a GK MB200 to a 1001 RB-II. Back in the 80's I did have one loaded with JBL's. From what I remember it sounded great.
 
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#13
@agedhorse just out of curiousity, how do you asses the mechanical power handling? I didn’t find the k140 spec’s in my winisd, and was to lazy to put them in. So I did not replicate your calculation. But my interest is in the general approach. Do you simply set the maximum at where the cone excursion graph exceeds x-max at a certain wattage for the input signal? Or do you allow some extra room for the fact that the actual input power will never be concentrated on one frequency? I myself allow some room for real world handling, but that’s for me diy-ing where I bear all the risk myself.
 
#14
@jwilson
JW56789 said:
Jackie: I see virtually no mention of Sarno products here in TB. Any insights? How do you like yours?
Click to expand...


Brad Sarno is small, independent builder in St. Louis. He builds products, from what I can tell, that mostly hit two main categories - pedal steel players and guitar players who are chasing the Jerry Garcia sound. So everything he builds is designed to be clean and have a lot of head room.

I think his pre does what it’s supposed to. It gets that classic Fender sound, clearly, with no distortion. Plus it’s quiet. The whole unit is a 1u rack too.

I’ve never played an F2B, so I can’t compare them, but TB member, @edwinhurwitz is the one who turned me into this unit, and he probably has compared the two.

Brad is also a really nice and helpful person. When I’ve asked him questions, his response isn’t a sales pitch, which is refreshing. I also purchased his Earth Drive, because while the classic pre is super clean, which I want most of the time, sometimes I want that dirtier sound - like a bunch of sunn cabs being pushed to the brink, and the Earth Drive can do that.

So I recommend it, but I can’t fairly give it a comparison to the other “Fender style” preamps out there.
 
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#15
jackietreehorn said:
Hello. I got a really good deal on an unloaded Peavey 115 BW cab. I'd like to drop a JBL K140 into it.

I don't know the first thing about power handling and tuning bass cabs and what not and I've tried reading the threads, and here is what I know, vs what I've figured out:

The cabs dimensions are 27" x 24" x 12.5" and it has a 6" round port. My terrible math skills calculate the volume of the cab at 4.69 cubic feet.

I've read JBL recommends 4 cubic feet tuned to 40 hz.

Will this cab work alright? More importantly, if install the JBL into this cab and take it out for a test drive to see how it sounds, I'm not going to damage it am I? (Please forgive my complete ignorance on this subject). Thanks.
Click to expand...

Ironically Peavey states that a majority of the Black Widow cabinets were 4 cubic feet tuned to 40Hz

Which would be the same as the recommended volume which JBL recommends for the K140.

Im not sure if your 27x 24x 12.5 is external or internal measurements
you would want to use internal dimensions.
 
#18
jackietreehorn said:
Those are external measurements. It makes sense that calculations are done on internal measurements though.

My thought process when I picked up this cab was that I know the Black Widow is supposed to be modeled after a JBL, so I was hoping it would be sized properly.
Click to expand...


Like many 15" speakers
The K140 and the Black Widow work well in 85 to 113 liters
or 3 cubic feet to 4 cubic feet.

The reflex or port tuning would be set close to the speaker Fs ( resonate frequency)

Black Widows Fs would range from about 42 to 46 Hz except for one special design which went down to 30 Hz

Any data I have seen claim the K140 and E140 Fs to be around 30 to 32 Hz

Having modeled those speaker in the past usually tuning from 38 to 43 Hz works well.

Also having a smaller volume around 85 to 90 liters or 3 to 3.2 cubic feet works well
for the E140 and K140. Helps to improve power handling or reduces how fast the speaker reaches
mechanical distortion.

Sounds like your Peavey Box is likely around 3.2 to 3.4 cubic feet.
Which is a very friendly volume for a K140
 
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#19
Assuming the cabinet is using 19mm or .75" material
you would subtract 1.5" from all you external dimensions for material depth.

27" - 1.5" = 25.5"
24" - 1.5" = 22.5"
12.5 -1.5" = 11"

So internal would be 25.5 x 22.5 x 11

Except the front baffle is likely setback for a grill.
probably around 1.25 " .....so

25.5" x 22.5" x 9.75"

3.273 cubic feet
91.67 liters
 
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#20
A small magnet 15" speaker would displace about 2 liters
and very large magnet speakers like a K140 would be about 4 liters

Also a 6" port with a length of 5" would displace 2.3 liters

So assuming 91.67 liters and subtracting 6.3 liters for the speaker and port

83.37 liters or 2.944 cubic feet

Depending upon end factor correction a single 6" x 5" length round port would yield a tune of around 52 to 54 Hz

If you wanted lower tuning around 42 to 45 hz you would want that port to be around 9 to 9.5 inches length
 
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